The hypervisor is the "core" for XEN itself. It gets booted by the boot
loader and controls cpu and memory, sharing them between your
administrative domain (Domain 0) and the virtual guest systems.
.
In order to boot a XEN system along with this package you also need a
kernel specifically crafted to work as the Domain 0, mediating hardware
access for XEN itself.

xen-utils-4.1:
No summary available for xen-utils-4.1 in ubuntu quantal.